This is a touchy subject in the baby sign language community, and only because you are probably talking to the wrong person! I for one do not sign every time I say a word. My stance is that I know how to sign the word, and also say it verbally. This gives me options. However, my baby must sign each word because he can’t say it otherwise. Between you and me, he understood this. Did he forget to sign occasionally? Maybe, it’s really hard to tell. Sometimes he would whine instead of signing, but I suspect this would have occurred regardless. When he wanted something and we prompted him, he would always sign. Perhaps he would have had better communication patterns had we been better role models, however, he did reach 125 signs by 17 months with 50 spoken words, so was far from suffering from our approach.
So in other words, not signing every word works for us, but it might not work for you. If
you really want to do it right, then please, by all means sign every word you want your baby to sign.
I do however believe that whatever course of action you take, it should suite your needs. Having said that, search deep down inside and decide for yourself what your goals really are. For me and my wife, signing was about empowering our son to be able to communicate with us, and not so that he would become a signer throughout his life. What he does with signing after he starts talking is entirely up to him. We did however abide by the signs of ASL, so that if he came across other signers or caretakers who signed, they’d be able to understand him. If he didn’t do the sign perfectly, we’d continue to model the correct sign for him, hoping he would eventually do it correctly. This is the ultimate reason why you should continue to sign to your baby after he has picked up a sign.
However, what we personally did was drop the signs as soon as he did an acceptable sign approximation. To us, and I believe to most signing parents, signing is a means to an end. We wanted to connect with our son, build his vocabulary and self esteem, pick his brain when he’d otherwise be voiceless, and have a fun time doing it.
What you will soon grasp, or might have already experienced, is that babies have an exceptional receptive language capacity. That is, while they can’t speak, baby’s understand almost exactly what you mean. This does permit you to get lazy with signing and simply use your voice to communicate leaving the signs entirely up to them. So that’s the short answer, you don’t have to continue to sign after your baby has successfully picked up a sign, but if you want to be the perfect role model and build your child into the perfect signer, then you should. I personally don’t sign each time, sometimes I do, and sometimes I don’t. To some babies, this might set a bad example, and they might choose not to sign, but my son signed exactly when he wanted and needed to, so it was no big deal. If you find that your child tends to follow your lead and reduce or eliminate signs because you don’t sign each time, then you might just have to suck it up and sign alongside them. Signing tells baby that using the sign is how communication is done, if Mom and Dad do the signs, then signing is something that is always done and so they will do it too. The call is yours!